1. Field of the Invention
The present invention relates in general to metallic powdered blends, and more particularly to a new and improved metallic powdered blend useful for making a vehicle part such as a valve seat insert.
2. Description of the Related Art
The operation cycle of an internal combustion engine is well known in this art. The physical requirements for the intake and exhaust valves, valve guides, and valve seat inserts to effectively interact in sealing the combustion have been studied extensively.
Wear resistance is a prime requirement for valve seat inserts used in internal combustion engines. In an effort to achieve a combination of good heat and corrosion resistance and machinability coupled with wear resistance, exhaust valve seat inserts have been made from cobalt, nickel, or martensite iron based alloy castings. These alloys have been generally preferred over austenitic heat-resistant steels with high chromium and nickel content because of the presence of wear resistant carbides in the cast alloys.
Powder metallurgy has been employed in the manufacture of valve seat inserts as well as other engine components, because the net end shape is fairly readily achieved. Powder metallurgy permits latitude in selecting a variety of metallic or even ceramic compositions as well as offering design flexibility.
U.S. Pat. No. 4,724,000 assigned to the Assignee of the present invention and hereby incorporated by reference describes a wear resistant article manufactured using powder metallurgy. This patent is particularly directed to a valve seat insert.
U.S. Pat. No. 5,041,158 also relates to powdered metal parts and particularly the beneficial affects of the addition of a powdered hydrated magnesium silicate. This patent is also assigned to the Assignee of the present invention and hereby incorporated by reference.
Other patents of interest include: U.S. Pat. Nos. 4,546,737; 4,671,491; 4,734,968; 5,000,910; 5,032,353; 5,051,232; 5,064,610; 5,154,881; 5,271,683; and 5,286,311.
Valve seat inserts for internal combustion engines require high wear resistance materials which can offer high wear resistance even at elevated temperatures for prolonged periods of time. Valve seat inserts further require along with the high heat resistance, high creep strength and high thermal fatigue strength even under repeated impact loading at elevated temperatures.
Typically, the valve seat insert materials that are made from high alloy powders have low compressibility. Therefore, processes such as double pressing, double sintering, high temperature sintering, copper infiltrating, and hot forging are used to achieve a desired density level. Unfortunately, this can make the material prohibitively expensive.
Thus, there still exists a need for a powdered metal blend which will result in a relatively high density, and yet only utilize a single press and/or a single sintering method. Such a material blend will be capable of being compacted to a minimum density ranging from about 6.7 g/cm.sup.3 to about 7.1 g/cm.sup.3 to make a component that can function in a severe engine environment. Such a powder metal blend will be fairly cost effective yet still offer significant wear resistance, high temperature resistance, machinability, high creep strength, and high thermal fatigue strength.